The Choke Coils
The Choke Coils.–Each of these is made by winding about 100 turns of
No. 28, Brown and Sharpe gauge, cotton covered magnet wire on a spool
2 inches in diameter and 2-1/2 inches long, when it will have an
inductance of about 0.5 _millihenry_ [Footnote: A millihenry is
1/1000th part of a henry.] at 1,000 cycles.
The Milli-ammeter.–This is an alternating current ammeter and reads
from 0 to 250 _milliamperes_; [Footnote: A _milliampere_ is the
1/1000th part of an ampere.] and is used for measuring the secondary
current that energizes the plate of the oscillator tube. It looks like
the aerial ammeter and costs about $7.50.
The A. C. Power Transformer.–Differing from the motor generator set
the power transformer has no moving parts. For this transmitting set
you need a transformer that has an input of 325 volts. It is made to
work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the
range of voltage of the ordinary alternating lighting current. This
adjustment for voltage is made by means of taps brought out from the
primary coil to a rotary switch.
The high voltage secondary coil which energizes the plate has an
output of 175 watts and develops a potential of from 350 to 1,100
volts. The low voltage secondary coil which heats the filament has an
output of 175 watts and develops 7.5 volts. This transformer, which is
shown in Fig. 81, is large enough to take care of from one to four 5
watt oscillator tubes. It weighs about 15 pounds and sells for $25.00.
[Illustration: Fig. 81.–Alternation Current Power Transformer. (For
C. W. Telegraphy and Wireless Telephony.)]
[Illustration: The Transformer and Tuner of the Worlds Largest Radio
Station. Owned by the Radio Corporation of America at Rocky Point near
Port Jefferson L.I.]
Connecting Up the Apparatus.–The wiring diagram Fig. 82 shows clearly
how all of the connections are made. It will be observed that a
storage battery is not needed as the secondary coil of the transformer
supplies the current to heat the filament of the oscillator. The
filament voltmeter is connected across the filament secondary coil
terminals, while Kykc 100 Mhz Byng the plate milli-ammeter is connected to the mid-taps
of the plate secondary coil and the filament secondary coil.
[Illustration: Fig. 82. Wiring Diagram for 200 to 500 Mile C.W.
Telegraph Transmitting Set. (With Alternating Current)]
A 200 to 500 Mile C. W. Telegraph Transmitting Set.–Distances of from
200 to 500 miles can be successfully covered with a telegraph
transmitter using two, three or four 5 watt oscillator tubes in
parallel. The apparatus needed is identical with that used for the 100
mile transmitter just described. The tubes are connected in parallel
as shown in the wiring diagram in Fig. 83.
[Illustration: Fig. 83.–Wiring Diagram for 500 to 1000 Mile C. W.
Telegraph Transmitter.]
A 500 to 1,000 Mile C. W. Telegraph Transmitting Set.–With the
apparatus described for the above set and a single 50 watt oscillator
tube a distance of upwards of 500 miles can be covered, while with two
50 watt oscillator tubes in parallel you can cover a distance of 1,000
miles without difficulty, and nearly 2,000 miles have been covered
with this set.
The Apparatus Required.–All of the apparatus for this C. W.
telegraph transmitting set is the same as that described for the 100
and 200 mile sets but you will need: (1) one or two _50 watt
oscillator tubes with sockets;_ (2) one _key condenser_ that has a
capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one
_0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5
amperes, and (5) an _A. C. power transformer_ for one or two 50 watt
tubes.
[Illustration: Broadcasting Government Reports by Wireless from
Washington. This shows Mr. Gale at work with his set in the Post
Office Department.]
The Alternating Current Power Transformer.–This power transformer is
made exactly like the one described in connection with the preceding
100 mile transmitter and pictured in Fig. 81, but it is considerably
larger. Like the smaller one, however, it is made to work with a 50 to
60 cycle current at 102.5 to 115 volts and, hence, can be used with
any A. C. lighting current.